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Date:   Mon, 31 Jan 2022 09:01:14 -0800
From:   Roman Gushchin <guro@fb.com>
To:     Waiman Long <longman@redhat.com>
CC:     Johannes Weiner <hannes@cmpxchg.org>,
        Michal Hocko <mhocko@kernel.org>,
        Vladimir Davydov <vdavydov.dev@gmail.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Vlastimil Babka <vbabka@suse.cz>,
        <linux-kernel@vger.kernel.org>, <cgroups@vger.kernel.org>,
        <linux-mm@kvack.org>, Shakeel Butt <shakeelb@google.com>,
        Muchun Song <songmuchun@bytedance.com>
Subject: Re: [PATCH 1/3] mm, memcg: Don't put offlined memcg into local stock
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References: <20211001190938.14050-1-longman@redhat.com>
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On Sun, Jan 30, 2022 at 10:55:56PM -0500, Waiman Long wrote:
> On 10/1/21 19:51, Roman Gushchin wrote:
> > On Fri, Oct 01, 2021 at 03:09:36PM -0400, Waiman Long wrote:
> > > When freeing a page associated with an offlined memcg, refill_stock()
> > > will put it into local stock delaying its demise until another memcg
> > > comes in to take its place in the stock. To avoid that, we now check
> > > for offlined memcg and go directly in this case to the slowpath for
> > > the uncharge via the repurposed cancel_charge() function.
> > Hi Waiman!
> > 
> > I'm afraid it can make a cleanup of a dying cgroup slower: for every
> > released page we'll potentially traverse the whole cgroup tree and
> > decrease atomic page counters.
> > 
> > I'm not sure I understand the benefits we get from this change which
> > do justify the slowdown on the cleanup path.
> > 
> > Thanks!
> 
> I was notified of a lockdep splat that this patch may help to prevent.

Would you mind to test this patch:
https://www.spinics.net/lists/cgroups/msg31244.html ?

It should address this dependency.

Thanks!